package configreader

import (
	"bufio"
	"fmt"
	"net"
	"os"
	"os/exec"
	"strings"

	"quickip/internal/model"
)

type Service struct{}

func New() *Service { return &Service{} }

func (s *Service) Read(interfaceName string) (model.InterfaceConfig, error) {
	iface, err := net.InterfaceByName(interfaceName)
	if err != nil {
		return model.InterfaceConfig{}, err
	}

	config := model.InterfaceConfig{Interface: interfaceName, DNS: []string{}}
	addrs, err := iface.Addrs()
	if err != nil {
		return model.InterfaceConfig{}, err
	}
	for _, addr := range addrs {
		ipNet, ok := addr.(*net.IPNet)
		if !ok || ipNet.IP.To4() == nil {
			continue
		}
		config.IP = ipNet.IP.String()
		config.Prefix, _ = ipNet.Mask.Size()
		break
	}

	config.Gateway = readGateway(interfaceName)
	config.DNS = readDNS()
	return config, nil
}

func readGateway(interfaceName string) string {
	cmd := exec.Command("ip", "route", "show", "dev", interfaceName)
	output, err := cmd.Output()
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(output), "\n") {
		line = strings.TrimSpace(line)
		if !strings.HasPrefix(line, "default via ") {
			continue
		}
		parts := strings.Fields(line)
		if len(parts) >= 3 {
			return parts[2]
		}
	}
	return ""
}

func readDNS() []string {
	file, err := os.Open("/etc/resolv.conf")
	if err != nil {
		return []string{}
	}
	defer file.Close()

	result := make([]string, 0, 2)
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if !strings.HasPrefix(line, "nameserver ") {
			continue
		}
		parts := strings.Fields(line)
		if len(parts) >= 2 {
			result = append(result, parts[1])
		}
	}
	return result
}

func MustRead(interfaceName string) model.InterfaceConfig {
	config, err := New().Read(interfaceName)
	if err != nil {
		panic(fmt.Sprintf("read interface config failed: %v", err))
	}
	return config
}